Detection of Structural Variants in Circulating Cell-Free DNA from Sarcoma Patients Using Next Generation Sequencing

Simple Summary Accurate diagnosis of sarcoma can be difficult as there are over 100 different subtypes. Approximately one third of sarcomas are characterised by subtype-specific genetic variants, which are routinely detected by the molecular testing of tumour biopsies. Recent studies have shown the potential use of next generation sequencing (NGS) for variant detection in circulating tumour DNA (ctDNA), which is DNA released from tumour cells into the bloodstream. Our feasibility study is the first to demonstrate the application of a custom NGS gene panel, targeting genetic variants in several sarcoma subtypes using ctDNA samples. Circulating tumour DNA (ctDNA) analysis using next generation sequencing (NGS) is being implemented in clinical practice for treatment stratification and disease monitoring. However, using ctDNA to detect structural variants, a common occurrence in sarcoma, can be challenging. Here, we use a sarcoma-specific targeted NGS panel to identify translocations and copy number variants in a cohort of 12 tissue specimens and matched circulating cell-free DNA (cfDNA) from soft tissue sarcoma patients, including alveolar rhabdomyosarcoma (n = 2), Ewing's Sarcoma (n = 2), synovial sarcoma (n = 2), extraskeletal myxoid chondrosarcoma (n = 1), clear cell sarcoma (n = 1), undifferentiated round cell sarcoma (n = 1), myxoid liposarcoma (n = 1), alveolar soft part cell sarcoma (n = 1) and dedifferentiated liposarcoma (n = 1). Structural variants were detected in 11/12 (91.6%) and 6/12 (50%) of tissue and plasma samples, respectively. Structural variants were detected in cfDNA at variant allele frequencies >0.2% with an average sequencing depth of 1026x. The results from this cohort show clinical potential for using NGS in ctDNA to aid in the diagnosis and clinical monitoring of sarcomas and warrant additional studies in larger cohorts.